The advent of soft contact lenses containing hydrophilic polymers had led to greatly increased comfort and usability. However, concommitantly with these improvements, the related problem of proteinaceous material absorbed into the lens, causing opaqueness, and sometimes infection, has arisen. Because soft contact lenses absorb up to approximately 150% of their weight in water, this absorbed liquid carries with it the protein content of tears, which protein content, over relatively short periods of time, results in lens opacity.
Since it was known that a major contributor to the opacity problem was, in fact, proteinaceous, it was logical to propose the use of proteases in cleaning solutions. Indeed, U.S. Pat. No. 3,910,296 discloses and claims the use of protease-containing solutions for soft contact lens cleaning. In addition, this disclosure suggests the use of sulfhydryl-group-containing compounds to "activate" the protease, presumably by reduction of the disulfide bonds contained in it.
A fair number of disclosures have sought to improve on the basic idea of a protease-containing cleaner, either by suggesting additions of other substances to the cleaning solution or by adjusting the conditions under which cleaning occurs, or both. For example, U.S. Pat. No. 4,096,870 suggests the use of a mixture of proteases with carbohydrases and lipases, such as that found in the digestive aid pancreatin. Addition of boric acid and sodium chloride to the cleaning composition is also suggested. U.S. Pat. No. 4,285,738 suggests the use of a hypertonic solution of urea and/or a guanidine salt in addition to the protease. This composition also contains a sulfhydryl compound or other reducing agent capable of cleaving disulfide bonds. British patent No. 2,019,721 is directed to cleaning compositions containing lipolytic enzymes in phosphate buffer. These compositions may also contain a proteolytic enzyme. Similar compositions are disclosed in British patent No. 2,029,225, European patent No. 5131, and Canadian patent No. 1,146,881. Mixtures of a protease with nonionic wetting agents are suggested in German application No. 2,854,278, published Mar. 7, 1980. A foaming version of a cleaner-containing protease is suggested by Japanese application No. 57/048,712, published Mar. 20, 1982, and the combination of papain and lactose in cleaning compositions is disclosed in British application No. 2,088,581, published Sept. 6, 1982.
Solutions which are free of "activators"--i.e., which do not contain sulfhydryl compounds capable of cleaving disulfide bonds--are disclosed in European patent application No. 140,669, published Aug. 5, 1985. These compositions contain protease extracts from various bacteria, such as bacillus, streptomyces, or aspergillus, and thus contain a variety of proteases, as well as, in some embodiments, amylase and lipases. European patent application No. 141,607, published May 15, 1985, improves on the basic proteolytic process by altering the treatment conditions by conducting the cleaning at an increased temperature. Particularly adaptable to cleaning carried out at these increased temperatures may be the heat-stable enzyme mixtures disclosed in PCT application No. 85/03247, published Jan. 8, 1985. These compositions contain such enzymes as thermolysin, caldolysin, and endopeptidase extracted from bacillus. Japanese application No. 60/196,722 discloses the mixture of amphoteric surfactants with various hydrolases, including proteases.
As with most applications, it is desirable to have available a variety of possible cleaning solutions, some of them better for particular lens compositions than others. The present invention offers another member of this group wherein the proteolytic activity of the basic protease content of the composition is improved by the addition of enzyme capable of exposing a target protein, lysozyme, for further cleavage.